Muscle exerciser



FIG. 1 is a perspective view of a muscle exerciser incorporating my new design;

FIG. 2 is a rear view of the muscle exerciser;

FIG. 3 is a right side view of the muscle exerciser with the opposite view being the same; and,

FIG. 4 is a bottom view of the muscle exerciser. 

The ornamental design for a muscle exerciser, as shown and described. 